1. Field of the Invention
The present invention relates to a process for the production of an epitaxially coated semiconductor wafer, composed of a substrate wafer of monocrystalline silicon having a front side and a rear side and at least one layer of semiconductor material which is epitaxially deposited on the front side of the substrate wafer. The invention also relates to a semiconductor wafer which can be obtained by the process.
2. The Prior Art
Epitaxially coated semiconductor wafers and their production are described, for example, in DE-4,119,531 A1. The production comprises the deposition of epitaxial layers on substrate wafers which were cut from a monocrystalline ingot which was pulled by the so-called Czochralski process from a melt contained in a quartz crucible. These monocrystals and the substrate wafers obtained therefrom, which are hereinafter termed CZ monocrystals and CZ substrate wafers, respectively, are contaminated with oxygen originating from the crucible material. The contamination with oxygen is utilized by generating oxygen precipitates by thermal treatment of the substrate wafers, which oxygen precipitates act as so-called internal getters and, in particular, bind metallic impurities to themselves. In this way, the layer epitaxially deposited on the substrate wafer can be kept substantially free of metallic impurities. This is particularly important since electronic structures and components whose serviceability is considerably disturbed by extraneous metal atoms are provided in this region of the semiconductor wafer.
The production of heavily doped CZ monocrystals having low resistivity is, however, very expensive and, in particular, it also presents technical problems in the case of doping with phosphorus. In particular, for process reasons, it is not possible to produce a CZ monocrystal which is uniformly heavily doped with phosphorus. Specifically, it is, as a rule, unavoidable that the dopant concentration in the monocrystal decreases axially and the resistivity increases axially. For this reason, some of the CZ substrate wafers produced from the monocrystal cannot be used as heavily doped substrate wafers. This output loss naturally also has a disadvantageous effect on the price which has to be paid for epitaxially coated semiconductor wafers based on heavily doped CZ substrate wafers.